The Mexican army discovered several clandestine graves holding at least 20 bodies near a ranch in the northern border state of Chihuahua, authorities said Monday.

Soldiers found the bodies of 19 men and one woman buried in 12 graves over the weekend in the town of Puerto Palomas, across from Columbus, New Mexico, and informed police so they could oversee excavations, Chihuahua state prosecutor Jorge Gonzalez said.

Gonzalez said that the bodies had been buried between four and eight months and that it had not yet been determined how they were killed because they were badly decomposed.

Earlier this month, the bodies of 18 men who were kidnapped in Acapulco where they had gone on vacation were found in a mass grave outside the resort city. An alleged drug trafficker arrested last week in Mexico City told police he ordered the killings after mistaking the men for members of a rival cartel.

Also in Chihuahua state, gunmen in two trucks chased and killed the newly appointed female police chief of the town of Meoqui on Monday. Hermila Garcia Quinones was driving to work when the attackers opened fire on her car, said Carlos Gonzalez, a spokesman for the state attorney general's office.

No one was arrested and no suspects were named.

Garcia became police chief Oct. 9 after a new mayor took office. Garcia, a former prosecutor, had never been a police chief before and authorities said she was the first woman to hold that post in Meoqui.

Chihuahua state, across the border from New Mexico and Texas, is one of the states most affected by drug violence and has recently seen an increase in the number of women leading police departments after men rejected the jobs out of fear.

In Praxedis G. Guerrero, east of Ciudad Juarez, 20-year-old university student Marisol Valles Garcia was named police chief in October. Valles Garcia's predecessor was shot to death in July 2009 and the town had no police chief until the young woman accepted the job.

Spreading Violence

Two other municipalities near Ciudad Juarez, which is sits across the border from El Paso, Texas, have also sworn in women as police chiefs.

In the Pacific coast state of Michoacan, gunmen killed the deputy police chief of the port city of Lazaro Cardenas, authorities said. Joaquin Garcia Gomez was at a gas station when assailants attacked him Sunday night, state prosecutors said in a statement Monday.

Police commanders, mayors and other leaders have increasingly become targets of drug gangs that are seeking to control territory for their operations, particularly in northern areas. More than 28,000 people have died in drug-related violence since President Felipe Calderon ordered a crackdown on gangs when he took office in December 2006.

On Monday, the Inter-American Press Association urged Calderon in a letter signed by hundreds of newspaper readers from throughout the Americas to find those responsible for the killing of a newspaper Mexican reporter.

The group asked Calderon to help move forward the investigation into the killing of Armando Rodriguez, who was shot in front of his daughter in Ciudad Juarez two years ago.